Flow separation in a variable-area subsonic and transonic turbulent channel flow

We have numerically investigated the flow separation dynamics in a subsonic and transonic channel flow undergoing a sinusoidal contraction of the cross-sectional-area. A block-spectral high-order unstructured code, H³AMR, is used to perform direct numerical simulations (DNS) for a frictional Reynolds number of Re_τ, 375. The size of the separation bubble is studied for four different blockage ratios between 10%-40%. The extent of the flow separation is investigated as a function of the local Mach number and pressure-gradient parameter. The results show a longer separation bubble for transonic flow conditions. In addition, proliferation of Q-isosurfaces are observed for transonic Mach numbers which is consistent with the increase of turbulence intensity after the reattachment.